The present invention relates to a focusing screen holding device for a single-lens relex camera.
The focusing screen in a single-lens relex camera is used to form an optical image through a mirror thereby to conduct focusing and framing. For this purpose, it is necessary to mount the focusing screen at a position equivalent to that of the emulsion layer of the film. However, because of dimensional tolerances of various components, it is impossible to mount the focusing screen at an accurate position directly upon assembling the components. That is, it is always necessary to adjust the position of the focusing screen.
Typical examples of a conventional focusing screen adjusting device are shown in FIGS. 1 and 2.
In the case of FIG. 1, a pentaprism 1 is fixedly secured to a prism support 3 which is fixedly secured to portions 2a and 2b of the camera body. A focusing screen 4 is supported by a focusing screen frame 5. The frame 5 is supported through springs 14 on portions 2c and 2d of the body in such a manner that it is urged upwardly as viewed in the figure by the springs and the position of the frame 5 can be adjusted by adjusting screws 12.
With this device, focusing adjustment can be satisfactorily carried out. However, the conventional focusing screen adjusting device is disadvantageous in the following points: The adjustment of the focusing screen position must be carried out before the dial, the winding lever, etc. on the upper cover are attached during assembly of the camera, and therefore the degree of freedom in assembling the camera is considerably small. In addition, in repairing or adjusting a camera, the adjustment of the focusing screen position cannot be accomplished without removing relatively many components. Furthermore, if dust sticks onto the focusing screen 4, it cannot be removed without removing and disassembling essential components such as the pentaprism 1 and the prism support 3 of the camera. Moreover, if the focusing screen 4 is scratched, it cannot be replaced without disassembling many components of the camera.
In the case of FIG. 2, a pentaprism 1 is secured to a prism support 3 which is fixedly secured to portions 2a and 2b of the camera body. A leaf spring 6 connected to a focusing screen frame 5, which supports a focusing screen 4, depresses the prism support 3, thereby urging the focusing screen frame 5 downwardly as viewed in FIG. 2. On the other hand, the focusing screen frame 5 is pushed upwardly in FIG. 2 by a focusing adjusting screw 8 which is supported by a mirror box 7 secured to portions (not shown) of the camera body. With this construction, after the camera has been completely assembled, adjustment of the focusing screen position as well as the adjustments of the dimensional errors of other components, is carried out by adjusting the focusing adjusting screw 8 with a screwdriver inserted througn an opening in a mount 9. However, this conventional focusing screen adjusting device is also disadvantageous in that dust cannot be removed from the focusing screen 4 and a scratched focusing screen 4 cannot be replaced without removing or disassembling relatively many components.